A judge has refused to grant permission for baby Indi Gregory to receive specialist treatment in Rome.
Mr Justice Robert Peel ruled that it was in the 8-month-old's "best interests" to die in the UK instead.
The verdict echoes the position of doctors treating Indi at Queen's Medical Centre in Nottingham who believe nothing more can be done for her.
Baby Indi is battling a rare mitochondrial disease. The Bambino Gesù Paediatric Hospital in Rome had offered to provide treatment for Indi that would be fully funded by the Italian government.
Indi's father, Dean Gregory, said the decision not to allow her to go to Rome for treatment was "sickening" and the family would appeal.
"Even if the transfer to Italy involves some risk, the only alternative we have been offered in the UK is to go along with Indi's death. There is nothing to lose for us or for Indi," he said.
"The offer from Italy is the only offer of treatment that we have, and as Indi's parents, we are prepared to take a risk to make that happen.
"Given that the medical evidence suggests she has a reasonable chance to survive and to improve, we believe it is in her best interests to be given that chance.
"We continue to be horrified at the [Nottingham University Hospitals NHS] Trust and UK courts' refusal to give her that chance."
Andrea Williams, chief executive of the Christian Legal Centre, said: "There is a hospital prepared to care for Indi in Rome. Indi's parents desire to give her every chance they can. Why would anyone try to stop this happening for them and for her?
"To deny them this opportunity is unimaginable, unjust and perverse.
"We stand with the family as they continue to fight courageously for their precious daughter's life."